Soils contaminated by, for example, hydrocarbons can often be remediated, that is cleaned, by forcing air (and thus oxygen) through wells into the contaminated underground regions. This injection may be in conjunction with the introduction of other gases, liquids or micro-organisms.
Soil remediation systems may also use forced air venting, also called soil vapor extraction (SVE). With this technique gas within the unsaturated contaminated soil matrix is extracted using vacuum applied at one or more extraction wells. Pressure gradients within the unsaturated zone induce a convection air flow through the porous soil matrix. The extent of the vacuum influence is determined by the soil properties. As the contaminated soil gas is removed, clean air from the surface is drawn into the contaminated zone; thus organic compounds to be volatilized, depending upon their vapor pressures.
Current SVE methods use gasoline, electric or hydraulically-driven positive displacement blower systems to pull the air and volatilized compounds from the wells. The typical blower system consists of a positive-displacement blower driven by a drive motor, a vacuum breaker, pressure relief valve, temperature switches, pressure and temperature gauges, intake filters and exhaust silencers. These SVE systems are typically mounted on skids since they are very heavy and they will only be left in place for a short period of time. There are several problems with conventional SVE systems. The blowers are noisy, and they are notorious for their inefficiency. Conventional SVE systems are expensive to purchase, to operate and to maintain. At the end of the clean-up procedure, SVE's must be disposed of. Vapor exhausted from the blower is above about 180.degree. Fahrenheit, posing a safety concern. Conventional SVE systems require large diameter piping between the blower skid and the wells. This above ground piping creates obstacles as well as being unsightly. Below grade piping is expensive and may require cutting through concrete slabs. A conventional SVE system often requires use of a crane to set up the system and typically entails a complicated startup procedure. Because of their many problems and drawbacks, potential users often decide against installing skid mounted SVE systems.
Conventional air injection systems suffer from many of the same drawbacks as conventional SVE systems.